Rhomboidal blades are used as rotor blades and guide vanes in axial turbo engines, such as turbines and axial compressors. These rhomboidal blades are characterized by a blade footing, whose cross section has the shape of a rhomboid or parallelogram with sides of equal length or with unequal sides in pairs. The advantage of this cross-sectional shape is that more blades can be accommodated on the circumference of the rotor or stator of the axial turbo engine than in the case of blades with a rectangular blade footing.
The manufacturers of the engines have always used a hot-rolled, rectangular flat steel or wide flat steel as the input stock for manufacturing the blades, from which the blade was machined by working from the solid. The rectangular flat or wide flat steel can be manufactured simply and consequently at a reasonable cost according to the rolling technology. If certain minimum amounts are purchased, the manufacturer is ready to deliver dimensions according to the customer's wishes. The length of the blade must always be arranged in the direction of rolling in all bars for reasons of strength. In the normal case, the rectangular flat steel is determined according to the maximum dimensions of the blade plus oversize for machining. Only one blade is arranged in the bar. The rectangular flat steel is then machined all around to obtain the desired rhomboidal cross-sectional shape of the blade. Depending on the size of the rhomboid angle, very much material must be removed by machining until the desired blade blank is obtained.
Smaller blades are manufactured by some engine manufacturers from wide flat steels. A plurality of blades are arranged next to one another in the bar. The wide flat steel is cut by oblique sawing into a plurality of rhomboidal parts corresponding to the number of blades, and these parts are then milled to the dimensions of the desired blade blank. The advantage of the wide flat steels is their flexible use for a plurality of blade types and the associated savings in terms of storage costs. Due to the possibility of sawing the wide flat steel into rhomboid bars, material and machining costs are saved compared with manufacture from a standard flat steel. The fact that the machining time for sawing and milling the bars is still long, on the whole, is a drawback.